Various types of analytical tests related to patient diagnosis and therapy can be performed by analysis of a liquid sample taken from a patient's bodily fluids, or abscesses. These assays are typically conducted with automated clinical analyzers (ACAs) onto which tubes or vials containing patient samples have been loaded. The analyzer extracts a liquid sample from the vial and combines the sample with various reagents in special reaction cuvettes or tubes (referred to generally as reaction vessels). Usually the sample-reagent solution is incubated or otherwise processed before being analyzed. Analytical measurements are often performed using a beam of interrogating radiation interacting with the sample-reagent combination, for example, turbidimetric, fluorometric, absorption readings, or the like. The measurements allow determination of end-point or rate values from which an amount of analyte related to the health of the patient may be determined using well-known calibration techniques.
Clinical chemistry analyzers employ many different processes to identify analytes and, throughout these processes, patient liquid samples and samples in combination with various other liquids (such as reagents, diluents, or re-hydrated compositions) are frequently required to be mixed to a high degree of uniformity. The uniformity of a sample should be achieved before sample transfer and ideally maintained throughout the processing of samples, including those that naturally separate over time (e.g., whole blood). Additionally, due to increasing pressures on clinical laboratories to increase analytical sensitivity, there continues to be a need for improvements in the overall processing efficiency of clinical analyzers. In particular, sample analysis continuously needs to be more effective in terms of increasing assay throughput.
The general trend in the ACA market is to convert manual tasks to automated tasks where possible. The level of automation achieved to date varies by the sample being used. For example, urine samples may require very little manual handling, whereas whole blood samples (i.e., blood samples having cells in suspension with serum and plasma) have traditionally been handled differently, requiring an operator to shake samples to suspend blood cells before an automated diagnostic step. This manual step can lower efficiency and can be a failure point in sample processing. The additional handling needed for whole blood diagnostics of patient samples in the in-vitro diagnostics (IVD) industry also makes it difficult to converge sample diagnostics for whole blood and other samples, such as urine or blood components into a single ACA process.
Assays performed by the IVD industry are commonly referred to as “blood work” because the patient is sampled and the specimen is sent to a laboratory for testing. The main types of samples used in IVD testing are serum, plasma, urine, whole blood, and cerebral spinal fluid. Serum, plasma, and whole blood samples are all taken the same way via a needle that is connected to a blood collection tube. However, different sample tubes are commonly used for different tests which require serum, plasma, or whole blood specimens that contain different additives that are required to avoid interferences and get the desired sample consistency. Serum and plasma, rather than whole blood samples, are used in a majority of clinical chemistry tests for blood because red blood cells can cause interference in some diagnostic reactions and because the blood plasma or white blood cells contain many analytes being measured. Serum and plasma can be created by spinning blood samples in a centrifuge to separate red blood cells out in the bottom of the tube.
Whole blood samples are primarily used in assays where the analyte measured is attached to the red blood cells or where the red blood cells themselves are being sampled. On a laboratory clinical chemistry system, there are a few assays that utilize whole blood as a sample, including HbA1c (measuring the ratio of hemoglobin A1c, glycated hemoglobin in erythrocytes), ethanol, glucose, immunosuppressive drug (ISD) tests, such as cyclosporine (CSA), tacrolimus (TACR), and sirolimus (SIRO), and various hemoglobin assays. “Whole blood assays” can refer to any subset or super-set of these assays. In addition to ACAs, a laboratory can use whole blood-specific instruments, such as hematology and coagulation instruments, to perform certain whole blood assays, such as assays focused on measuring red cell count, clotting, and other macroscopic properties of whole blood. Certain assays may be incompatible with hematology and coagulation instruments or may be more suitable for ACAs. For example, immunoassays require detection technology that is most similar to serum/plasma immunoassays already available in ACAs (e.g., immunoassays generally require a reaction to take place with antibodies and a precise detection of the resulting concentration of an analyte).
Typically, ACAs are not designed to automatically handle whole blood samples. Whole blood samples are commonly collected in a Potassium EDTA salt containing tube that acts as an anti-coagulant. The sample should not clot and should be uniform prior to any transfer or analysis taking place. Even without clotting, differences in density between red blood cells and the surrounding components cause whole blood to gradually separate, with the denser red cells going to the bottom of the tube and lighter white blood cells and blood plasma staying on the top. The cells in the sample can typically be re-suspended by mixing. Mixing of the contents to re-suspend the fluid typically must to be gentle enough to avoid foaming the sample. One common mixing technique requires a laboratory technician to gently invert the tube by hand to mix it. This manual task can be somewhat automated using a simple bench top device called a sample nutator, which is typically separate from an ACA or other diagnostic device.
Some chemistry systems get around the handling of whole blood by manually pre-treating the blood with a lysing agent, typically diluting the whole blood specimen on the bench, to allow a supernatant sample to be drawn off. This sample can then be handled the same way as serum or plasma samples because these lysed components will no longer settle over time like an untreated whole blood sample. Lysing may be undesirable or impractical because it is generally only suitable for specialized low volume testing due to the amount of manual interaction with the sample and potential for human error.
A typical ACA includes mechanical mixing components for mixing solutions and samples, but these components are not designed specifically for handling whole blood samples. For example, once a sample is placed into a reaction vessel, such as a cuvette, a sample or reaction probe can be moved in a mixing pattern. Such a mixing process can introduce foaming to a viscous sample, such as whole blood. It also requires proper hardware, such as an ultrasound transducer, attached to a probe to allow rapid horizontal translation. However, mixing within the ACA can only re-suspend blood cells in the sample in the particular vessel being mixed. In the instance of whole blood, if the sample used to draw an aliquot was not fully mixed prior to aliquoting, the ratio of red blood cells to plasma and serum will not be representative of the sample, which can introduce error into subsequent assays.
Therefore, there remains a need to reliably mix samples that naturally separate over time, such as whole blood, at the time of aliquot transfer and to further verify the uniformity of the sample. To fully deliver the automation advantages of an ACA, it is desirable to provide a process that does not require a separate nutator or manual mixing step. There is a further need to address this issue without adding hardware to existing ACAs, to improve automation on existing setups.